Desulfurization process



Filed July 26, 1960 Inventor William J. Mo'rox United States Patent O 3,128,155 DESULFURIZATION PROCESS William Judson Mattox, Baton Rouge, La., assignor to Esso Research and Engineering Company, a corporation of Delaware Filed July 26, 1960, Ser. No. 45,309 3 Claims. (Cl. 23-284) The present invention concerns an improved process for removing sulfur, nitrogenous or metallic contaminants from petroleum fractions, such as fuel oil, shale oil, residua, reduced or whole crudes. More particularly, the present invention relates to the use of molten potassium hydroxide containing from 5 to 30 Wt. percent water, based on total reagent, to remove from heavy petroleum fractions the sulfur, nitrogenous, and metallic contaminants contained therein. In addition, the invention relates to a process for regenerating the potassium sulde formed during desulfurization to potassium hydroxide for reuse as an impurity removal agent.

The problem of sulfur removal from petroleum fractions and crudes goes back to the inception of the petroleum industry. For most purposes, it is undesirable to have an appreciable amount of sulfur in any petroleum product. Gasoline should be relatively sulfur-free to make it compatible with lead. Motor fuels containing sulfur as mercaptans are undesirable because of odor and gum formation characteristics. Sulfur is objectionable in fuel oils because upon combustion sulfur dioxide, a corrosive gas having an obnoxious odor, is formed. Metropolitan areas have been particularly conscious of air pollution problems caused by sulfur-containing fuels and in certain instances have restricted by law the amount of sulfur permissible in fuel oils utilized in the locale.

Generally sulfur occurs in petroleum stocks in one of the following forms: mercaptans, suldes, disuldes and as part of a more or less substituted ring, of which thiophene is the prototype. The mercaptans are generally found in the lower boiling fractions, e.g., the naphtha, kerosene, and light gas oil. Numerous processes for sulfur removal from these lower boiling fractions have been suggested, such as doctor sweetening (wherein mercaptans are converted to disuldes), caustic treating, solvent extraction, copper chloride treating, etc., all of which give a more or less satisfactory decrease in sulfur or inactivation of mercaptans by their conversion into disuldes. When the process results in the latter effect, the disuldes generally remain in the treated product and must be removed by another step if its is desired to obtain a sulfurfree product.

Sulfur removal from higher boiling fractions, however, has been a much more difcult operation. Here the sulfur is present for the most part in the less reactive forms as suldes, disuldes and as a part of a ring compound, such as a thiophene. Such sulfur is, of course, not susceptible to chemical operations satisfactory for removal of mercaptans. Extraction processes employing sulfurselective solvents are also unsatisfactory because the high boiling petroleum fractions contain such a high percentage of sulfur-containing molecules. For example, even if a residuum contains only about 3% sulfur it is estimated that substantially all the molecules may contain sulfur. Thus, if such a residuum were extracted with a solvent selective to sulfur compounds the bulk of the residuum would be extracted and lost ICC Metallic contaminants, such as nickel and vanadium compounds, are found as innate constituents in practically all crude oils. These contaminants present another problem. Upon fractionation of the crudes, the metallic contaminants are concentrated in the residua which normally have initial boiling points of about 1000o F. Such residua are conventionally used as heavy fuels, and it has been found that the metal contaminants therein adversely affect the combustion equipment in which the residua are burned. The contaminants not only form ash, which leads to sludging and the formation of deposits upon boiler tubes, combustion chamber walls, and gas turbine blades, but also attack the refractories which are used to line boilers and combustion chambers and severely corrode boiler tubes and other metallic surfaces with which they come into contact at high temperatures.

The nitrogenous compounds are found in many crude oils to a varying extent depending on the source. These compounds are objectionable primarily due to (l) their tendency to promote instability in the finished, marketable products, such as gasoline, kerosene, heating oil, jet fuels and the like regardless of whether these are obtained by simple distillation procedures or by cracking heavier fractions and (2) due to their adverse effects on the activity of catalytic materials used in cracking reactions, etc.

In the past, methods to chemically remove the sulfur have been ineffective to remove large amounts of sulfur and furthermore, had little or no effect on the nitrogenous or metallic impurities, these material requiring other methods for their removal.

It is an object of the instant invention to provide an improved method for removing sulfur, metallic and/ or nitrogenous impurities from petroleum fractions, even the heavier petroleum fractions, such as heavy fuel oil, residuum, etc. It is a further object of the instant invention to provide a means for regenerating the spent impurity removal agent.

It has now been discovered that the above objects may be accomplished by contacting the petroleum fraction with molten potassium hydroxide containing from about 5% to about 30% water, based on total mixture, under temperature conditions within the range of about 350 F. to 800 F. The molten potassium hydroxide reagent containing 5 to 30% water used in accordance with the present invention is not uid at normal atmospheric temperatures and in order to produce a fluid and a useable reagent it is necessary to heat the reagent substantially above atmospheric temperatures to obtain the fluid or liquid molten potassium hydroxide. It has further been found that the potassium hydroxide in admixture with barium hydroxide will also effectively remove the sulfur, metallic and nitrogenous impurities in the petroleum fraction. It has further been found that the addition of a solutizer selected from the group of compounds which may be described as oil soluble organic compounds of carbon, hydrogen, and oxygen which form alkali metal compounds, such as alcohols, phenols, alpha and beta naphthols, isobutyric acid, etc., also improves the action of the molten KOH reagent of the instant invention.

Furthermore, it has been discovered that partial hydrogenation of the feed prior to contacting said feed with the molten KOH containing water, quite unexpectedly further improves the effectiveness of the molten KOH reagent. In addition, it has been found that by the use of steam at temperatures within the range of 400 to 1000 Vdrocarbon oil, thus yielding a high quality product.

F. the potassium sulfide formed during the desulfurization of the heavy petroleum fraction may be regenerated to potassium hydroxide which may be reused for further impurity removal.

The exact nature and additional objects of the instant invention will be more readily understood by referring to the accompanying drawing and the detailed description of the specific embodiment of the process which the accompanying drawing exemplifies.

AFeed, such as a 950 F.-|- Kuwait residuum, is obtained from a suitable source and directed via line 1 into hydrotreating zone 2 where the feed is subjected toa partial hydrogenation step which renders the feed more susceptible to the subsequent treatment with molten potassium hydroxide containing specific amounts of Water. Within the hydrotreating zone, the residuum from line 1 contacts hydrogen entering Via line 3 and a hydrotreating catalyst, such as cobalt-molybdate-alumina, or various oxides and/or suldes of cobalt, molybdenum, chromium, nickel, iron, etc. either supportedl or unsupported or any other suitable known hydrogenation catalyst. The operating conditions in hydrotreating zone 2 are usually within the temperature range of about 200 to 600 F. and at pressures in the range of about 100 to 1000 p.s.i.g. The gas from hydrotreating Zone 2, which will consist primarily of unused hydrogen and H28, is withdrawn through line 4. The partially hydrotreated oil is Withdrawn via line 5 and sent to impurity removal zone 6.

The partial hydrogenation which occurs in zone 2 is to be distinguished from a complete hydrogenation step by both the operating conditions employed therein and the resultant treated product. l Operating conditions are chosen so as to effect a hydrogen consumption of about ,25 to 50% of the amount the oil is capable of consuming under more severe conditions. This partial hydrogenation may be favored by higher feed rates, lower hydrogen partial pressures, lower temperatures, etc. than those normally used to promote maximum hydrogen consumption.

Although a hydrotreating step has been shown in the drawing, it will be understood that sulfur, metallic and and nitrogenous impurities may be removed merely by directing the feed to the impurity removal zone Without any prior partial hydrotreating. The hydrotreating step in combination with the impurity removal step is merely a preferred embodiment of the instant invention.

, The invention in its broadest form relates to the step which occurs in the impurity removal zone 6. The residuum, after partial hydrogenation in thisrembodiment, is contacted with molten potassium hydroxide containing specific amounts of Water entering through line 7. The residuum and molten KOH are intimately mixed which causes the sulfur, metallic and nitrogenous impurities in the residuum to react with the potassium hydroxide and to form products which may be removed from the hy- Impurity removal zone 6 may be a batch operation wherein the oil and aqueous molten KOH are intimately mixed, or it may be desirable that this step be carried on continuously, for example, by countercurrently contacting the molten KOH containing water with the residuum or other feed being treated.

The amount of water in the molten potassium hydroxide is critical for the improved results of the instant invention. The water content should be within the range of about 5 to 30 wt. percent based on total reagent, preferably 7 to 25 wt. percent. Temperature conditions during the contacting step should be maintained within the range of about 350 to 800 F., preferably 400 to 650 F. The amount of molten potassium hydroxide reagent (including water) may be within the range of 25 to 200 Wt. percent of the feed being treated, preferably 50 to 150 wt. percent in order to provide adequate contact. It is to be understood that only a Very small proportion of this potassium hydroxide is converted to K2S and thus the reagent is suitable for use in treating additional oil before regeneration is required. Treating time may be as little as 1/10 hour but generally the longer the time of contact the greater the impurity removal, so it is preferred to employ treating times within the range of 1A to 2 hours.

The mixture of KOH and hydrocarbon material leaves the impurity removal zone through line 8 and passes t0 settling zone 9 where in the unreacted molten KOH containing water separates as a distinct phase from the treated residuum phase, which will contain varying proportions of the reaction products of impurities and molten KOH. A distillate fraction such as gasoline, heavy naphtha, kerosene, heating oil, etc. or any suitable fraction boiling below about 700800 F. may be introduced through lines 21 and 8 to facilitate oil-molten KOH separation. This step will not usually be required except in treating very heavy, viscous, residual type oils. Thus, part of molten KOH phase recovered from settling zone 9 may be directed via lines 26, 11 and 7 back to zone 6 `forreuse while part is passed through lines 26 and 10 to hydrolysis zone 12 for regeneration of K2S to KOH. The hydrocarbon phase passing from zone 9 through line 22 will contain some of the inorganic reaction products formed in the impurity removal zone 6. Wash water is introduced through line 23 to extract these materials and in electrical precipitation zone 24, or in some other suitable separation equipment, the aqueous extract phase is separated from the treated oil, which is removed through line 25. If the extract water from zone 24 contains KZS as the main impurity, this material is Withdrawn from zone 24 by line 10 and combined with the spent caustic in line 26 and passed to hydrolysis zone 12 for regeneration to KOH. Heavy metal impurities, such as nickel, Vanadium, etc. which may be present in the aqueous extract from zone 24, may conveniently be removed by ion exchange, selective precipitation, filtration, etc. before passage to zone 12.

Settling zone 9 will preferably be maintained at or near the temperature held in impurity removal zone 6 in order to` facilitate gravity separation of oil and reagent and prevent heat loss from the caustic entering hydrolysis zone 12. n

In hydrolysis zone 12 the predominantly molten caustic phase has steam bubbled therethrough at a temperature in the vrange of about 400 to 1000 F., converting the K25, which is the reaction product of the potassium hydroxide and the sulfur impurities, to potassium hydroxide. An excess of steam over that required to react stoichiometrically with the KZS will be employed and will usually be within the range of about 10 to 30 mols of steam per mol of sulfide per hour. Pressures may vary from 4near atmospheric to about 300 to 500 p.s.i. and may be Vregulated to assist in the control of caustic concentration withdrawn through line 15.

The hydrolyzed mixture is sent via line 15 to settling zone -18 where the potassium hydroxide will separate from any remaining hydrocarbon phase and may be withdrawn via line 17 and recycled to the impurity removal zone through line 7. Any oil product withdrawn through line 1'6 may be combined with that from line 25l or may be used as desired.

Preferably a solutizer is present during the impurity removal step. For example, it may be added to zone 6 via. line 20 or mixed with the feed or the molten KOH reagent prior to their entering the impurity removal zone.. These compounds consist of oil soluble organic compounds of carbon, hydrogen, and oxygen which form `alkali metal compounds inthe presence of strong alkali and may be used in concentrations of about 0.1 to 10 wt. percent based 'on the oil. These materials Will be recovered in the spent caustic removal from zone 9 and in the aqueous phase from zone 214. During hydrolysis in zone 12, 'these solutizers will be removed from the caustic and recovered for reuse through line 14. Nitrogenous impurities picked u-p from the oil by the caustic may also be liberated through line 14. Fur-ther quantities of nitrogen may be removed lfrom the system as NH3 or other volatile compounds through line l25 with the treated oil.

The molten KOH reagent in the instant invention may be used in admixture with barium hydroxide, barium hydroxide monohydrate or mixtures thereof. The proportion of barium hydroxide, etc., to potassium hydroxide may vary widely, but usually -will be within the range of about 5 Ito 50 wt. percent of total reagent. Such mixed reagents may be used not only to promote the desulfurization reaction but also to increase the rate of hydrolysis of sulfide to hydroxide since barium sulfide is more easily hydrolyzed than the potassium suldes. `In general, the operating conditions employed in impurity removal zone 6 or in hydrolysis zone 12 when using the mixed hydroxide reagent will not differ 4:greatly from that ordinarily used for molten KOH. Approximately the same levels of water content in the reagent will also be employed.

EXAMPLE l Batch tests were made on a 950 IFl-l- Kuwait residuum containing 5.2f Nvt. percent sulfur with molten KOH containing Water to determine the effect of varying the amount of KOH, the water content thereof, the temperature conditions and the treating time. The individual tests were conducted by adding the indicated amount of potassium hydroxide to the `oil at 300 to 400 F. with stirring, increasing the temperature to the designated level and maintaining it there for the specified time with continuous high speed mechanical stirring. After cooling to about Z50-300 FF., xylene or other comparable hydrocarbon was added to facilitate separation of oil from potassium hydroxide and the diluent removed yfrom the treated product by distillation. In some instances where KZS remained suspended in the oil, the sulfide was decomposed witfh acid preceding the removal of the xylene. The results are shown in Table A below:

Table A EFFECT 0F OPERATING CONDITIONS ON DESUL- FURIZATION AND DEMETALIZATION WITH MOLTEN KOH-H2O MIXTURE EFFECT OF AMOUNT OF KOHeHzO MIXTURE Table A--Continued EFFECT 0F WATER CONTENT 0F MOLTEN KOH EFFECT 0F TEMPERATURE EFFECT 0F TREATING TIME 1 A very conservative extrapolation of the data. 2 Initial water content; some loss during treat.

-From the above table it is clear that these variables all effect the desulfurization of the residuum. Thus it is necessary that the amount of molten KOH reagent be within the range of 25 to 200 wt. percent yof feed being treated, preferably 5 0 to 150` |wt. percent. The rwater coritent of the molten KOH should be Within the range of 5 to 30 wt. percent, preferably 7 to 25 wt. percent. The optimum Water content would be about 15 Wt. percent water. As is seen above, the temperature substantially affects the desulfurization obtained and the temperature during contacting should be in the range of about 350 to 800 F., preferably 400 to 6150" IF. Furthermore, the longer the treating time the more the desulfurization, but treating time less than 1 hour may be used. It is preferred, however, that treating times within the range of .about 1A to 2 hours be employed.

EXAMPLE 2 This experiment was conducted to demonstrate the large removal of Vsulfui and metals which is obtained by use of the molten KOH containing -water of lthe instant invention. The experiments were conducted in two physically dierent environments; namely7 an autoclave and an open beaker. Three different feeds were tested. In two runs the autoclave was used to avoid loss of light hydrocarbons Ifrom theV more volatile feeds. Contacting and oil recovery in both the autoclave and open beaker tests 'were accomplished by the same general pro- T t Wtt. pHer Wt. pter- T T t lercerlit Perclnt cedure as described in Example l.

ES C011 3 CGD GUID., TG3 GS11 el i No. in KOE KOH on o F Hours hmm moved The results of the experiments are given in Table B R20 Feed tion below with the temperature and contact time of each run. Mlxture In each test the molten KOH contained l5 wt. percent 898 15 34 600 4 `water based -on total reagent and the reagent was present gg-jj: 15 100 600 4 in equal amounts by Weight to the feed being treated. 876.-- 15 200 600 4 Only traces of -gas or coke were formed during these tests.

Table B METAL AND SULFUR REMOVAL WITH MOLTEN KOH-H2O REAGENT Contacting Vessel Nickel-Lined Autoclave Open Beaker Feed 400 F,+ Heavy 700 F.-| Kuwait 950 F.+ Kuwait 650 F.+ Heavy Lake Mix. Lake Mix. Treating Temperatures, 650 700 600 600. Contact Time, Hours 2. 5 4.0 4.0 2.

Feed Product Feed Product Feed Product Feed Product Inspections:

Vanadium, p.p.m 400 20 40 5 90 Percent Removed 88 Sulfur, Wt. Percent 2. 5 2.0 4. 2 2.9 5. 2

Percent Removed 20 31 Nickel, p.p.m

.Percent Removed It may be seen from the above table that the molten KOH-H2O reagent employed Within the conditions of the instant invention is an excellent Idesulfurization and demetalization agent.

EXAMPLE 3 A 950 F.-| shale oilV bottoms fraction was contacted for lfour lrours at 600o F. with molten KOH containing 15% water, based on total reagent, in a manner similar to lthat used in Example l. The nitrogen content of the shale oil Was decreased from 2.7 Wt. percent to 1.9 wt. percent, representing `a nitrogen reduction of 30%.

EXAMPLE 4 Potassium sulfide recovered from desulfurization operations, such as described in the above examples, by gravity settling -and/ or water washing was placed with Water in a steel autoclave, heated to the designated temperature, and steam passed through the sullide at a predetermined rate. Excess steam in the eluent gas was condensed and the HZS therein, adsorbed in a caustic, was determined by well-known analytical procedures. From the quantity of HZS liberated during the steaming, the yamount of hydrolysis -was calculated. The effects of various temperature levels on the hydrolysis of K2S when employing 30 mols of steam/mol or sulde/hour are shown in the following table:

Table C HYDROLYSIS OF ALKALI METAL SULFIDES AT 30 MOLS STEAM/MOL SULFITE/HOUR Test No 890 S88 S91 894 889 Temperature, F 400 600 750 800 900 Percent Kgs Hydrolyzed in First Hr. 20 33 76 84 99 Mols Steam employed/Mol B2S liberated 152 94 40 36 30 Operating now at 750 IF. ,and varying the steam/K25 mol ratio `it will be seen in Table D below that high conversion to KOH may be lob-tained with less mols of steam/mol of HZS liberated.

Table D KZS WITH STEAM EFFECT OF STEAM] HYDROLYSIS OF SULFITE RATIO AT 750F.

Percent KZS Mols Steam Test N o. Mol Ratio of Hydrolyzed employed] Steam to K1S in rst Hr. Mol H28 liberated EXAM-PLE 5 A 95 0 R+ Kuwait -residuum was treated vvith molten GOH containing water with and Without the presence of beta-naphthol. In the latter, the sulfur removal was 47% at 600 F. With the beta-naphtllol present the sultur removal was increased to 59% at the same temperature and other operating conditions. In each case, the molten KOH containing water :amounted to wt. percent of oil being treated. The quantity of beta-naphthol was 10 wt. percent based on oil. Contacting and Workup procedures were 4the same as in Example 1 except in the test with naphthol wherein `a small amount of the solutizer which remained in the treated oil was removed by volatilization with steam.

It is .apparent that the presence of beta-naphthol increases the effectiveness of the molten KOH containing water and thus it is preferred in the instant invention to remove the impurities in the presence of a solutizer, such as beta-naphthol. The solutizers applicable to the instant invention include a wide varie-ty of oil soluble organic compounds of carbon, hydrogen, and oxygen which form alkali metal compounds in the presence of strong alkali, especially such compounds which contain one or more OH and/ or -COOH groups.

EXAMPLE 6 In treating a 950 F.l Kuwait residuum at 600 F. for 4 hours, one part of oil and one part of molten KOH containing water give 47% desulfurization and with two parts of the same KOH reagent no better desulfuriZa-tion was obtained. The percent of Water in the molten KOH was 15 wt. percent based on total reagent. In a similar experiment carried out at the same temperature conditions and for the same length of time one part of oil, one part of KOH and one part of barium hydroxide gave 64% desulfurization. Again the Water content was 15 Wt. percent based on total reagent. These evaluations were carried ont in the same way as described for Example 1 and demonstrate the more favorable extent of desulfu-rization which may be achieved with KOH-Ba( OH) 2 reagents as compared to that eccted with the same quantity of single-component reagent.

It is apparent that the presence of barium hydroxide with the aqueous molten KOH provides new and unexpected improved desulfurization of the oil. `It is thus a preferred embodiment of the instant invention to employ the molten KOH containing water lin combination with 5 to 50 wt. percent barium hydroxide based on total reagent to give further increased desulfurization.

Alternatively, the petroleum Ifractions may be desulfurized by contact with the molten potassium hydroxide containing water supported on :a mechanically strong material of fluidizable particle size. The particles with hydroxide thereon are maintained in a uidized state during the contacting step. Any alkali metal suldes which form on the iluidized solids may be reconverted to the hydroxide by steaming in the same zone or in a hydrolysis zone and the regenerated solids reused.

What is claimed is:

1. The process of regenerating `a molten potassium hydroxide reagent containing potassium sulfide and about 5 to 30 wt. percent water based on total reagent which comprises bubbling steam through said molten potassium hydroxide and potassium sulfide at va temperature in the range of about 400 to 1000 F. and a pressure in the range from about atmospheric to about 500 p.s.i. to hydrolyze the potassium sulfide in the reagent.

2. The process `of claim 1 wherein the hydrolysis reaction is carried `out a temperature of 750 to 900 F. and the ratio of steam employed in the hydrolysis reaction is 10 to 30 moles of steam per mole of potassium sulfide in the reagent being regenerated.

3. The process of claim 1 wherein the potassium hydroxide reagent which contains 5 to 3() wt. percent water based on total eagent also contains from 0.1 to 10 Wt.

percent of a solutizer.

References Cited in the file of this patent UNITED STATES PATENTS 10 Carb Nov. 24, 1931 Borden Dec. 30, 1941 Kalichevsky et -al Feb. 16, 1943 Ayers Feb. 10, 1948 Bond Aug. 17, 1948 Chenicke et a1. Nov. 4, 1952 Fear Mar. 15, 1960 Robbins et -al June 19, 1962 

1. THE PROCESS OF REGENERATING A MOLTEN POTASSIUM HYDROXIDE REAGENT CONTAINING POTASSIUM SULFIDE AND ABOUT 5 TO 30 WT. PERCENT WATER BASED ON TOTAL REAGENT WHICH COMPRISES BUBBLING STEAM THROUGH SAID MOLTEN POTASSIUM HYDROXIDE AND POTASSIUM SULFIDE AT A TEMPERATURE IN THE RANGE OF ABOUT 400 TO 1000*F. AND A PRESSURE IN THE RANGE FROM ABOUT ATMOSPHERIC TO ABOUT 500 P.S.I. TO HYDROLYZE THE POTASSIUM SULFIDE IN THE REAGENT. 